poj2631 树的直径 + bfs

 1 //Accepted    492 KB    0 ms
 2 //树的直径 bfs
 3 #include <cstdio>
 4 #include <cstring>
 5 #include <iostream>
 6 #include <queue>
 7 using namespace std;
 8 const int imax_n = 10005;
 9 struct node
10 {
11     int u,v,c;
12     node()
13     {
14 
15     }
16     node(int u,int v,int c):u(u),v(v),c(c)
17     {
18 
19     }
20 }p[2*imax_n];
21 int e;
22 int head[imax_n];
23 int next[imax_n*2];
24 void addEdge(int u,int v,int c)
25 {
26     p[e]=node(u,v,c);
27     next[e]=head[u];
28     head[u]=e++;
29 }
30 void init()
31 {
32     memset(head,-1,sizeof(head));
33     memset(next,-1,sizeof(next));
34     e=0;
35 }
36 bool vis[imax_n];
37 int dis[imax_n];
38 queue<int >q;
39 int bfs(int s)
40 {
41     int ans=0;
42     int temp_node;
43     while (!q.empty()) q.pop();
44     memset(vis,0,sizeof(vis));
45     q.push(s);
46     vis[s]=1;
47     memset(dis,0,sizeof(dis));
48     while (!q.empty())
49     {
50         int x=q.front();
51         q.pop();
52         if (dis[x]>ans)
53         {
54             ans=dis[x];
55             temp_node=x;
56         }
57         for (int i=head[x];i+1;i=next[i])
58         {
59             int y=p[i].v;
60             if (!vis[y])
61             {
62                 vis[y]=1;
63                 q.push(y);
64                 if (dis[x]+p[i].c>dis[y])
65                 dis[y]=dis[x]+p[i].c;
66             }
67         }
68     }
69     return temp_node;
70 }
71 int main()
72 {
73     int x,y,c;
74     init();
75     while (scanf("%d%d%d",&x,&y,&c)!=EOF)
76     //for (int i=0;i<5;i++)
77     {
78         //scanf("%d%d%d",&x,&y,&c);
79         addEdge(x,y,c);
80         addEdge(y,x,c);
81     }
82     x=bfs(1);
83     y=bfs(x);
84     printf("%d\n",dis[y]);
85     return 0;
86 }